DE2916747A1 - ELECTRIC INDUCTION MACHINE WITH EVAPORATION COOLING - Google Patents

Description

-5- WS164P-1951

Electric induction machine with evaporative cooling

The invention relates to an electric induction machine with evaporation cooling, in which a machine is provided with windings and via this downwardly protruding magnetic core is accommodated in a housing, the free inner volume of which is filled to a level below the windings with an insulating liquid that can evaporate at the operating temperature, and with one with the interior of the housing communicating storage tank for receiving a non-condensable at the operating temperature and the operating pressure Insulating gas, which depends on the vapor pressure of the insulating liquid in the housing inside from this is displaceable into the storage container, the non-condensable insulating gas at a first predetermined temperature essentially completely in the storage container and essentially completely at a second predetermined temperature is arranged in the housing interior, and further the first and second predetermined temperatures within the temperature range which the magnetic core and the windings assume during operation.

Fs / ai The

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The use of evaporative cooling in electrical induction machines, especially in power transformers, is known, wherein an insulating liquid is used which is in the range of normal operating temperatures Has evaporation point. The insulation liquid is supplied to the power transformer in liquid form and evaporates on the surface of the heat-generating part, an amount of heat being withdrawn from it which is equal to the latent Heat of vaporization is. The resulting vapors are then condensed and recirculated in the cooling circuit. In addition to the actual cooling properties, the insulating liquid also has the task of providing the necessary dielectric strength between the individual electrical elements in the vapor phase at normal operating temperature and partial pressure to ensure.

Since insulation fluids with these properties are extremely expensive, economic considerations require to limit the amount of liquid to a minimum. In known electrical induction devices with evaporative cooling becomes a relatively small amount of the evaporable insulation liquid in a sump volume at the bottom of the housing and fed from there with the aid of a pump to the heat-generating electrical windings (U.S. Patents 2,961,476 and 3,261,905).

Because the dielectric strength of the vaporisable insulation liquid is directly proportional to that acting inside the housing Pressure, a second insulating medium is usually added as an insulating gas, which is essentially at the operating temperature and operating pressures of the induction device

condensing

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can be denied. One such insulating gas is ζ. Β. Sulfur hexafluoride (SF ,,), which is added in sufficiently large quantities

is used to increase the dielectric strength between the electrical Elements inside the housing also when the system is switched on or under low load conditions runs. In this state, almost all of the vaporizable insulation liquid is in the liquid Phase, so that the dielectric strength of the insulating gas is ensured. When the temperature of the device the normal operating temperature approaches, the non-condensable insulating gas must be displaced from the housing and in one separate storage tanks are stored so that it does not interfere with evaporative cooling. Such a solution is known from U.S. Patents 2,961,476 and 4,011,535. Because the non-condensable gas is an essential part of the housing when switched off or when the load is low, a relatively large storage tank is required, thus the entire volume of the non-condensable gas from the free internal volume of the housing into the storage container can be displaced. As both the ratings and size of power transformers with evaporative cooling has increased significantly recently, this results in a relatively high volume requirement for the storage container due to the larger amount of the non-condensable gas required. This will make the Overall dimensions of the systems increased significantly. Although it is known the separation of the non-condensable To effectively provide insulating gas from the insulating liquid, no measures are known in these systems, due to whose the amount of non-condensable insulating gas and thus the size of the storage container can be reduced

can

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The invention is therefore based on the object for an electrical Induction machine with evaporative cooling to find measures that make it possible to reduce the volume of the storage tank for the non-condensable insulating gas compared to known arrangements, with small amounts of the flawless cooling is guaranteed. This object is achieved according to the invention solved in that the storage container has a volume, the size of which is proportional to the free internal volume of the housing as well the volume of the insulating liquid results from the following equation:

V - ^V E I ^K 1 ^V L

S KoKq

therein means:

VS is the volume of the storage tank

V "the free internal volume of the housing

plus the volume of the magnetic core and

of the windings

K. a constant which is equal to 0-1 / 1 - / "^ 0,

where 0 is a volume ratio of the non-condensable insulating gas that is absorbed per unit volume of the insulating liquid, and β is a ratio of the density of the vaporized portion to the density of the liquid portion of the insulating liquid, V _{T is} the volume of the insulating liquid K is a constant which is equal to 1- β / 1- β φ

K is a constant which is equal to TP / T ₀ P ₁ ,

ο 12 2 1

whereby

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where T _{1 is} the temperature and P is the partial pressure of the non-condensable insulating gas at the first predetermined temperature and T is the temperature and P is the parbial pressure of the non-condensable insulating gas at the second predetermined temperature

- That the bottom wall of the housing with a recess

is provided, which is the lower yoke of the magnetic core

receives, with the free space surrounding the yoke

Forms sump volume, which is the smallest possible amount

absorbs the insulating liquid.

The invention finds particularly advantageous use in a Power transformer, which is housed in a tightly sealed housing and made on a magnetic core

arranged phase windings consists. The bottom wall of the housing is provided with a recess into which the lower The yoke of the magnetic core protrudes, with the lower end face of the windings at a certain distance from the rest of the bottom wall is located. At least enough of the insulating liquid is filled into the interior of the housing that at least a part of the sump volume running around the lower yoke of the magnetic core is filled with the insulating liquid. Furthermore is in the housing that at normal operating temperatures and normal operating pressures. non-condensing insulating gas, which has the task of increasing the electrical breakdown strength between the conductive parts in to secure low load operation. During operation, the insulation liquid with the help of a pump from the. Sump volume sucked off and supplied to distribution devices, which have a uniform

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Ensure a moderate distribution of the liquid over the magnetic core and the electrical windings. Part of this insulation liquid evaporates when it is in contact with the heated parts Comes into contact, whereby the amount of heat corresponding to the latent heat of vaporization is dissipated. The non-condensable Gas is fed together with the vapor of the insulation liquid to a cooler, in which this is not the case condensing insulating gas collects above the condensed insulating liquid due to its lower density. This condensed Insulation liquid flows back into the housing, while the non-condensed gas flows into the storage container provided for this purpose is displaced. As soon as the load and thus the operating temperature decrease, the non-condensing insulating gas flows back into the housing and ensures that the dielectric strength between the electrical parts.

The lower yoke of the magnetic core can do this by means of appropriate structural configurations of the recess in the bottom wall of the housing affects completely surrounding sump volume and the volume between the lower end face of the windings and the bottom wall and be reduced. This reduction in volume eliminates the need for known packing and furthermore the prerequisite is created that the volume of the storage container for the non-condensing insulating gas is considerable can be reduced. Due to the arrangement of the lower yoke of the magnetic core in the recess, this is continuously bathed by the insulating liquid, so that the temperature of the magnetic core without an increase in the Amount of the vaporizable insulation liquid can be reduced. Because the insulation fluid is thus more efficient

ver

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is recycled, smaller amounts can be used., whereby the costs for the insulation liquid and thus for the cooling can be reduced significantly. on the other hand this contributes to the fact that the storage volume for the not condensable insulating gas can also be reduced. Finally, the immersion of the lower yoke provides the Magnetic core in the insulation liquid has the advantage that the magnetic core is effective as a heat source when switched on and already the evaporation of the insulation liquid triggers in the switch-on mode, so that the pumps conventionally used up to now are dispensed with that promote the insulation liquid due to the development of steam.

The advantages

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The advantages and features of the invention also emerge from the following description of exemplary embodiments in connection with the claims and the drawing. Show it:

1 shows a partially sectioned side view of an induction machine with evaporative cooling;

2 shows a partially sectioned side view of a further induction machine with evaporative cooling;

3 shows a section along the line III-III in FIG. 1;

4 shows a partially sectioned side view through a further induction machine according to the invention,

The induction machine 10 shown in Fig. 1 is constructed as a power transformer and housed in a housing 12, the housing walls 14, 16 and 18 has. This housing 12 surrounds the actual induction apparatus 22, which consists of a multilayered Magnetic core 24 and electrical windings consists. The magnetic core 24 is in turn made up of legs 30 and 32 constructed, which are each magnetically connected to one another via a yoke 26 and 28. These yokes run horizontally whereas the legs run vertically.

On the legs 30 and 32 windings 34 and 36 are arranged, which as a high-voltage winding and as a low-voltage winding are trained. The windings are made of a suitable electrically conductive material such as Aluminum or copper and can be either round or ribbon-shaped

or

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or also be plate-shaped, with them in individual Winding layers 30 are arranged around the legs 30 and 32 of the magnetic core 24. A plurality of cooling lines 40 are arranged between the individual winding layers 38, through which an insulation liquid 42, explained in more detail below, can flow for cooling purposes.

The windings 34 and 36 are connected in a conventional manner to an external electrical network via electrical lines and feed-through capacitors (not shown). Although only a single-phase transformer is shown for explanation, the invention is also for the person skilled in the art easily recognizable for multi-phase transformers or multi-phase Induction apparatus can be used and can also be used to cool reactors and other high-voltage electrical equipment Find use whenever evaporative cooling can be used.

The induction apparatus is filled with an insulating liquid cooled in the form of a two-phase dielectric liquid, the evaporation point of which is in the range of the normal working temperature of the induction apparatus 22 is located. The insulation liquid not only causes sufficient cooling in the Vapor phase, but also at normal working temperatures and pressures an electrical insulation of the individual Windings 34 and 36. As is generally known, inactive fluorinated organic compounds can be used as the insulating liquid Find use, such compounds being known from US Pat. No. 2,961,476. As these dielectric fluids are relatively expensive, it is necessary for economic reasons to use the amount

the

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to keep the insulation liquid as low as possible. For this reason, a small amount of the Insulation liquid 42 is provided up to a level 44 above the floor surface. Because only a small amount of the insulation liquid for cooling the power transformer 10 is used, suitable devices are available that recirculate the insulation liquid 42 over and over again via the windings 36 and 38. As can be seen from Fig. 3, For this purpose, a pump 46, a line 48 and a distributor nozzle 50 are arranged within the housing 12. With the aid of the pump 46, the insulation liquid 42 is pumped up from the lower region of the housing via the line 48 and evenly distributed over the windings 34 and 36 with the aid of the distributor nozzle 50. The insulation liquid flows in the process, through the cooling lines 40 within the windings 34 and 36 downwards. Although only a simple distribution nozzle 50 is shown in the drawing, any distribution device can be used for the distribution of the isolation liquid with which an even distribution of the insulation liquid over the surfaces to be cooled is guaranteed is.

In operation, the insulating liquid 42 is evenly used the distributor nozzle 50 distributed over the individual windings and the cooling lines 40 of the power transformer. Included the insulation liquid flows down through the cooling lines 40 and evaporates as a result of the windings 34 and 36 generated heat. An amount of heat corresponding to the latent heat of evaporation of the insulation liquid 42 is thereby generated dissipated from the windings. The resulting vapor of the insulation liquid 42 rises through the cooling lines 40 up into the housing 12, where it turns out to be condensate

at

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precipitates on the housing walls and flows back to the bottom surface 12. With the housing 12 is also an external cooler 52 connected, which can consist of a pipe cooler or some other suitable cooling device and via a line 54 is connected to the interior of the housing 12. The condensate produced in the external cooler flows through line 54 back into the interior of the housing 12 and can be circulated again for cooling purposes.

The insulation properties of the vaporous insulation liquid used are, in a known manner, directly proportional to the pressure and the temperature which are effective within the housing 12. If the power transformer is excited when it is initially switched on or operates with a low load, only a relatively small part of the insulating liquid 42 is converted into the gaseous or vaporous state, so that the dielectric strength between the individual conductor elements of the transformer may be inadequate. For this reason, a second insulation medium is used in conjunction with the insulation liquid 42, this insulation medium having a sufficiently high dielectric strength even in the case of low load conditions and when the power transformer is in the state of being. This insulation medium is typically gaseous and has no tendency to condense at the usual operating temperatures and operating pressures. _{Sulfur hexafluoride (SF R} ) can be used as such a gaseous insulation medium, this gaseous insulation medium filling up the essential part of the housing volume in the switched-off state.

When a load is applied to the transformer, insulation liquid is increasingly evaporated, which causes the

casing

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Housing 12 builds up an increasing vapor pressure. This vapor pressure causes the mixture to be non-condensable Gas as well as the evaporated insulation liquid flows from the housing 12 to the external cooler 52, in which the evaporated Isolation liquid is condensed and flows back into the housing 12. Since that's preferably used, don't condensable gas has a lower density than the insulating liquid in the vaporized state, the non-condensable gas increases Gas enters the upper part of the external cooler 52 and flows via line 56 into a suitable storage container 58, separating the vaporizable insulating liquid from the non-condensing gas during normal operation the power transformer is disconnected. If there is a drop in performance, the non-condensable gas will flow out of the Storage container 58 back into housing 12, thereby ensuring constant dielectric strength between the conductive Parts of the transformer is ensured. The storage container 58 is via a drain line 59 with the interior of the Housing 12 connected, so that any insulation liquid 42 that may have got into the storage container flow back to the housing 12 can.

In the illustration, a direct connection line 56 from the storage tank to the external cooler is shown, but can both the external cooler and the storage container are each independently connected to the interior of the housing 12 be. In this way, the non-condensable gas is returned from the external cooler 52 directly into the housing 12.

Since the non-condensable gas in the unloaded state of the transformer essentially takes up the inner volume of the housing 12

borrowed

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lichen completely filled out and there also under normal operating conditions the non-condensable gas is completely displaced into the storage container 58, this must be one Sufficiently high storage volume atxfweise to the total To be able to absorb proportion of the non-condensable gas. Increasing the power rating of transformers with evaporative cooling has led to very large housing dimensions in the past. For the same reason therefore, an additional amount of non-condensable gas is required to fully cover the interior of the housing to fill the non-condensable gas when the transformer is shut down or operated in the low load state. This made it necessary to significantly increase the overall dimensions of such Indukti ons systems to the to create the necessary volume. In many cases, however, such an enlargement is one because of other requirements Limit set.

Several basic considerations are made below: -to better understand the invention. The required volume of the storage container 58 for storage of the non-condensable gas is described by the following equation.

_v -

^V S

SK ₂ K ₃ - 1

Where: V ₁ -, the volume of the storage container 58

V is the free internal volume of the housing 12 including the external cooler and exclusively the volume of the induction apparatus

K. a constant from the value 0-1 / 1 $ 0, where 0 is the volume fraction of the non-cash condensable

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describes baren gas, which is absorbed in a unit volume of a certain insulation liquid 42. The quantity β describes the density ratio between the vaporous part and the liquid part of the insulation liquid

V is the volume of the insulation liquid 42 L.

No constant of size 1- / 3 / 1- / 3 0

Cl

K describes the expression Τ, Ρ, / Τ P "where T is the temperature and P _{1 is} the partial pressure in the non-condensable gas when there is no load and T" describes the temperature or P the partial pressure of the non-condensable gas under normal working conditions.

For temperatures below 30 C, which are within the normal operating temperatures of the induction apparatus described, B is relatively small and can be set equal to zero without the accuracy of the relationship being significantly affected.

With the help of the invention it should be achieved that smaller housings for electrical induction machines or induction apparatus with a smaller internal volume and thus a correspondingly smaller requirement for insulation liquid is required. the Reduction of the free internal volume and the volume occupied by the isolation liquid results in a even greater reduction in the required storage volume for the non-condensable gas. This allows the Reduce the overall dimensions of such electrical induction apparatus quite significantly.

From Fig. 1 it can be seen that the bottom wall 20 of the housing has a central channel-shaped recess 70, which extends over the entire length of the power transformer 10.

the

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The recess has a substantially U-shaped cross-section with a transverse wall section 72 and one each perpendicular wall section 74 and 76. The lower yoke 28 of the magnetic core essentially fits into the recess 24, with a certain sump volume 78 remaining free. There is essentially so much of the insulating liquid 42 used that the sump volume 78 filled and the lower Yoke 28 of the magnetic core is surrounded on all sides by the insulating liquid. Transverse ones close to the depression Wall sections 80 and 82, which merge into the side walls. In the transition area to the side walls it is closed ensure that the housing is absolutely tight. The lower end of the housing merges into flanges 84 and 86, which are used for support of the housing 12 are used.

The stepped design of the recess 70 moves the housing wall 20 closer to the windings 34 and 36, so that the distance between the bottom sections 80 and 82 and the lower end face of the windings is also substantial is decreased. This also results in a further reduction in the free internal volume in the housing 12 and accordingly a reduction in the need for the non-condensable gas and the insulation liquid. As already mentioned, This is accompanied by a significantly greater reduction in the storage container 58, since a reduction

3 of the internal volume of the housing is significantly larger by 1 cm Reduction of the volume in the storage container 58 allows.

The following example is described for explanation. A power transformer with 2500 kVA and evaporative cooling, at which the bottom wall 20 of the housing

flat

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is flat, typically has a free internal volume enclosing

3 lent the cooling volume of around I ₃ 33 m and would

3
Measured cooling need about O ₅ 18 m from the evaporable insulation liquid, whereby enough heat is generated to operate a pump. For the specified isolation fluids, 0 would have a value of about 6.7. In the case of a transformer of the same type with a structure according to the invention and a recess in the bottom area that receives the yoke of the magnetic core, the free internal volume is reduced

3 including the cooler to about 1, 26 m, being only about

3
0.11 m of the vaporizable insulation liquid is required. If you determine the volume ratio of the storage tank required for the two transformer arrangements and if you solve the above equation with the corresponding values, it follows that the volume of the required storage tank for the transformer according to the invention is 21% smaller than the corresponding volume for is the storage tank of the transformer with the flat bottom wall. This 21% reduction in volume with respect to the storage container is achieved by reducing only 5% of the free internal volume in the housing through the provision of the recess. In addition, the transformer according to the invention requires about 40% less insulation liquid, which, regardless of the reduction in the cost of the insulation liquid, also brings a reduction in the volume for the storage tank with it, since a smaller amount of insulation liquid also means a smaller amount of the non-condensable gas absorbed.

The bottom sections 80 and 82 according to FIG. 1 run essentially perpendicular to the vertically arranged wall sections 74

and

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and 76 of the recess 70. With such an arrangement the maximum reduction in the free interior space in the housing 12 can be achieved.

In the further embodiment shown in FIG. 2, the bottom sections 80 and 82 of the housing are inclined downward and do not merge perpendicularly into the vertical wall sections 74 and 76 of the recess. By this inclined Arrangement of the bottom sections ensures safe drainage of the condensed vapor of the insulation liquid into the sump volume 78 ensures in which the lower yoke 28 of the magnetic core 24 is arranged.

This embodiment is particularly advantageous when the Assembly takes place at the consumer and the lower end faces of the windings of the transformer do not run in one level. In such a case it can happen that the insulation liquid is due to different horizontal End faces in parts of the tank collects, especially if it is not set up completely flat and therefore uneven Cooling of the power transformer is triggered. This can be done with the help of the inclined floor sections Overcome the problem and ensure that the condensed insulation liquid drains off into the sump volume 78.

In Fig. 3, an embodiment is shown in which the channel-shaped recess 70 over the entire bottom width of the Housing 12 extends. The bottom surface of the recess, i.e. the wall section 72, does not run horizontally, but inclined slightly to one side. This slight inclination ensures that the insulation liquid flows in the direction of the pump 46 and the pump in the deepest

area

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Can be arranged area of the sump volume. This also allows the amount of insulation liquid required further decrease. Finally, a further embodiment of the invention is shown in Fig. 4, in which the recess 70 is limited by two further vertically extending wall sections and 95, so that a depression is formed, the bottom section of which 92 compared to the embodiment according to FIG. 3

further reduced by the length of the wall sections 96 and 97 is. This recess is just large enough to accommodate the yoke 28 of the magnetic core and a small one to accommodate the yoke to form sump volume 78 running around. The wall sections of the recess surround this yoke in a relatively small distance. As a result, the required amount of insulation liquid is further reduced very significantly. In this embodiment, the pump 46 is located outside of the sump volume and opens only with an intake port in the same.

By means of these measures of the invention, the free can according to the particular circumstances and requirements Significantly reduce the internal volume in the housing of an induction apparatus in those areas which are necessary for the determination the necessary amount of insulation fluid are important. Due to the reduction in the required Amount of isolation fluid reduces the volume of the storage container 58 for the non-condensable Gas even more, since a reduction in the internal volume of the housing results in a corresponding reduction of the volume of the storage container 58 by a factor of about 1.2 to about 2.5. By training the deepening and placing the lower yoke of the magnetic core

in this

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The yoke is immersed in the insulation fluid in this recess continuously, so that the temperature of this part of the magnetic core is continuously cooled without additional expenditure of insulating liquid. With the help of the invention the insulation liquid can be used much more effectively, so that only less for good cooling Liquid is needed. In addition, the lower yoke of the magnetic core immersed in the insulation liquid acts as a Heat source in start-up operation, which causes the insulation liquid to evaporate and therefore does not start up triggers mechanical, based on vapor pressure pumps, as proposed for such evaporative cooling became.

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eerse

it

Claims (8)

Claims (1. Electric induction machine with evaporation ^ Tcühlung, in which a magnetic core provided with windings and protruding downward over these is accommodated in a housing, the free internal volume of which is up to a level below the windings with a level that can be evaporated at the operating temperature Insulation liquid is filled, and with a storage container communicating with the interior of the housing for receiving a non-condensable insulating gas at the operating temperature and the operating pressure, which can be displaced from this into the storage container depending on the vapor pressure of the insulating liquid inside the housing, with the non-condensable insulating gas at a first predetermined temperature is arranged essentially completely in the storage container and, at a second predetermined temperature, essentially completely in the interior of the housing, and furthermore the first and second predetermined temperatures are arranged within the temperature range which the magnetic core and the windings assume during operation, characterized in that,
- That the storage container (58) has a volume, the size of which proportional 809 & 45 / 084O -2- WS164P-1951 proportional to the free internal volume of the housing (12) and the volume of the insulating liquid (42) by the following Equation gives: V S therein means: VS is the volume of the storage tank (58) V is the free internal volume of the housing (12) minus the volume of the magnetic core (24) and the windings (34, 36) K. a constant equal to 0-1 / 1 -A 0, where 0 is a volume ratio of the non-condensable Insulating gas is absorbed per unit volume of the insulating liquid (42) and is a ratio of the density of the evaporated Is part of the density of the liquid part of the insulating liquid V is the volume of the insulating liquid K is a constant which is equal to 1- β / 1- / 3 0 K is a constant which is equal to T ₁ P / TP ₁ , O X. Ct 2t X. where T is the temperature and P is the partial pressure of the non-condensable insulating gas at the first predetermined temperature and T is the temperature and P _{0 is} the partial pressure of the not Ct condensable insulating gas is at the second predetermined temperature - That the bottom wall (20) of the housing (12) is provided with a recess (70) which the lower yoke (28) of the magnet core (24) receives, wherein the free space surrounding the yoke forms a sump volume (78), which the smallest possible amount 909846/08 * 0 -3- WS164P-1951 absorbs the insulating liquid. 2. Electronic induction machine with evaporative cooling according to claim 1, characterized in that - That the recess (70) only partially with the insulating liquid is filled. 3. Electric induction machine with evaporative cooling according to claim 1 or 2, characterized in that - That the recess (70) has a substantially U-shaped cross-section and extends from one under the yoke (28) Bottom section (72; 90) and two vertically extending wall sections (74, 76) is formed, which in one Distance run laterally along the yoke. 4. Electric induction machine with evaporative cooling according to claim 3, characterized in that - That the bottom portion (72) is inclined to the horizontal plane. 5. Electric induction machine with evaporative cooling according to claim 3 or 4, characterized in that - that the vertically extending wall sections of the recess (70) merge into transverse bottom sections (80, 82), which are part of the bottom wall (20) of the housing (12). 6. Electric induction machine with evaporative cooling according to claim 5, characterized in that - That the transverse bottom sections (80, 82) are essentially perpendicular to the vertically extending wall sections (74, 76) of the recess (70) to opposite one another Housing walls (16) run. -4- WS164P-1951 7. Electric induction machine with evaporative cooling according to claim 5, characterized in that - dalj the bottom sections (80, 82) in the direction of opposite ones Housing walls (16) run with an increasing slope. 8. Electric induction machine with evaporative cooling according to one or more of claims 1 to 7, characterized marked inet, - That the vertical wall sections (74, 76, 94 ₃ 95) starting from a bottom section (90) run at a distance from the four sides of the lower yoke (28) of the magnet core (24), the bottom section (90) preferably following one Side is inclined, and - That the recess is inserted into the bottom wall (20) in such a way that around the recess horizontally or to the recess bottom sections (80, 82, 96, 97) of the bottom wall (20) which run inclined towards the bottom are formed. Ö0984B / 0840